WASHINGTON - The once and future front-runner, Mitt Romney, has labored back into position as the leader for the Republican nomination. On a Super Tuesday that yielded mixed results, Romney captured the states he needed to win, including Ohio, and expanded his formidable lead in delegates.

But the costs of his recovery after a rocky February have been considerable, both to himself and to his party. The former Massachusetts governor soon must reckon with the fallout of his sharp shift to the right and a harshly negative campaign, even while he continues to grind down the competition.

Calls are increasing for a unifying push behind Romney. Republicans know that the longer the acrimonious GOP primary continues into spring, the tougher it will be for the ultimate nominee to build strength for the general election campaign against President Obama. And the danger that the contest will continue for months is real, as Romney was on track Tuesday night to have secured just a quarter of the 1,144 delegates he would need to clinch the nomination.

“The Democrats are savoring every day it doesn’t come to a conclusion,’’ said former House speaker Dennis Hastert, a Romney supporter from Illinois. “You’re in a circle shoot, and everybody keeps taking potshots at everybody else.’’

The potshots have been flying for months, to widespread dismay. GOP grande dame Barbara Bush, at a conference in Dallas this week, called 2012 “the worst campaign I have ever seen in my life.’’

The GOP feud has damaged the public’s regard for all the candidates. Among crucial swing-vote independents, Romney’s negative rating soared to 48 percent in an ABC/Washington Post poll released Tuesday, compared with just 32 percent who viewed him favorably.

Respondents in an NBC/Wall Street Journal poll were asked to sum up the nominating battle, and 60 percent of the independents answered with a negative word or phrase. Some examples, as reported by NBC: “unenthusiastic,’’ “discouraged,’’ “painful,’’ “disappointed,’’ “poor choices,’’ “underwhelmed,’’ “uninspiring,’’ and “depressed.’’

Not exactly a recipe for success in November.

Despite the divisive primary, Romney, if he wins the nomination, may have little trouble uniting fractured Republicans behind him. That’s because of their mutual dislike of Obama, said Darrell West, vice president and director of governance studies at the Brookings Institution, the nonpartisan Washington think tank.

A greater challenge, after Romney’s recent lurch to the right, will be winning over independent voters who will ultimately decide the November election. Examples of Romney’s shift include a speech before a conference of conservatives last month in Washington, when he declared he is “severely conservative.’’

“He has provided so much video for the Democrats over the last two months,’’ said West. “Saying that he is ‘severely conservative’ - that phrase doesn’t have the same ring as ‘compassionate conservative’ that worked so well for [George W.] Bush. It reinforces the wrong message.’’

The candidate also has been drawn at times into the party’s ideologically fraught debate over insurance coverage for contraception, which dominated the agenda on the hustings and in the US Senate for several weeks.

Another trouble spot, West said, will be Latino voters, who have become a crucial bloc in the important general election swing states of New Mexico, Colorado, Florida, and Nevada.

Romney has taken a hard line against illegal immigration in the primary. A Fox News Latino poll released Monday showed that Obama had overwhelming support of Hispanics surveyed, 70 percent, to just 14 percent for Romney in a hypothetical matchup.

“One of the most damaging things he did was go far right on immigration,’’ West said.

Political consultants and analysts say tough primaries like this one can have a silver lining because they season the winning candidate for a general election. The prolonged Democratic primary campaign in 2008 between Obama and Hillary Clinton is widely believed to have given Obama crucial experience on the national stump and prepared him for the general election against John McCain.

Knoxville News Sentinel/Michael Patrick/AP

Election worker Rubye McGhee helped to prepare a polling place in Knoxville, Tenn., for primary voters Tuesday. The state had 55 delegates up for grabs in the Republican primary.

In the case of Romney in 2012, it remains unclear how much he will benefit from that phenomenon.

To be sure, he has demonstrated the ability to fight back aggressively when his back is against the wall. He rebounded from a loss to Newt Gingrich in South Carolina and won Florida with strong debate performances and a massive barrage of attack ads.

Rick Santorum shocked Romney with victories in Colorado, Minnesota, and Missouri. Romney struck back with hugely important wins in Michigan and Arizona.

But the seasoned veteran also has made unforced errors. Romney has been prone to high-profile gaffes about his own personal wealth that made him seem out of touch.

“Romney unfortunately doesn’t seem to have learned much since 2008. He keeps making the same mistakes that one would not expect a second-time presidential candidate to make,’’ said professor Michael McDonald, director of the United States Elections Project at George Mason University, in Virginia. “It’s inexplicable, because by now he should have learned not to make these gaffes.’’

A more tangible benefit of slogging through a heavily contested primary is the base of supporters Romney has now built up in the potential battleground states of Ohio, New Hampshire, Florida, and Michigan.

Those volunteers and get-out-the-vote telephone lists would serve Romney well in a general election.

The contested primary also has fueled media attention to attacks by Romney and the other candidates on Obama’s handling of the economy. For the most part, many of those attacks have gone unanswered by the president’s campaign, McDonald said.

“The Republican message is the one that dominates the airwaves,’’ McDonald said. “Voters in these states will have heard much more about what the Republican position is on most of the issues.’’

But the message must be the right message.

In the four weeks since Santorum shook the foundations of Romney for President Inc. with the trio of surprise victories, Romney allowed this most critical issue in the general election - fixing the economy, stupid - to slip to the back burner. Romney allies say the candidate needs to return to his plans to fix the economy and lead the party away from divisive debates about insurance coverage for contraception and religion in government life.

Emphasizing plans to create jobs would help Romney win over independents, moderates, and “Reagan Democrats’’ in November, asserted Hastert, who succeeded Gingrich as House speaker in 1999 and remained in the post until 2007.

“The Republican Party will never agree with itself on social issues,’’ Hastert said. “The one thing we can agree on is the economy.’’